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Publication numberUS3469489 A
Publication typeGrant
Publication dateSep 30, 1969
Filing dateMay 27, 1968
Priority dateMay 27, 1968
Also published asDE1918884A1
Publication numberUS 3469489 A, US 3469489A, US-A-3469489, US3469489 A, US3469489A
InventorsBarth Carl
Original AssigneeBarth Carl
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
System of movable frets for stringed musical instrument
US 3469489 A
Abstract  available in
Previous page
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Claims  available in
Description  (OCR text may contain errors)

C. BARTH Sept. 3011969 SYSTEM OF MOVABLE FRETS FOR STRINGED MUSICAL INSTRUMENT Filed May 27, 1968 A-r-romvevs United States Patent 3,469,489 SYSTEM OF MOVABLE FRETS FOR STRINGED MUSICAL INSTRUMENT Carl Barth, 2486 E. Skyline Drive, La Habra, Calif. 90631 Filed May 27, 1968, Ser. No. 732,227

Int. Cl. G101! 3/06 U.S. Cl. 84-314 9 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Field of the invention The invention relates to stringed instruments, and more particularly to fretted instruments in which the strings are pressed against the frets to control the note or chord produced when the strings are played.

Description of the prior art In a conventional fretted instrument such as a Spanish guitar, the desired notes and chords are produced by first depressing a particular string or group of strings into engagement with the associated frets of the guitar fingerboard, and thereafter striking, plucking or otherwise setting into vibration the guitar strings. The contact between the frets and the strings must be firm and solid to avoid vibrational interaction and objectionable buzzing noises. This in turn requires strong finger pressure on the strings, which alone is a considerable challenge to a beginner or student of the instrument. However, the problem of developing and maintaining adequate finger pressure is compounded by the characteristic necessity of having to stretch several fingers between widely spaced frets in order to play certain chords.

For example, where several strings must be pressed against selected frets on a conventional guitar, the fingers employed are arranged on the strings as close to the selected frets as possible to thereby minimize the amount of finger pressure required for solid fret contact. However, the length of the players fingers, distance between the selected frets, or need to crowd fingers into a small area often results in finger contact on one or more strings a significant distance from the fret to be employed. By the nature of the geometry in the fingerboard-to-string relationship, a depressed string engages the adjacent, unwanted fret first and it is then necessary to increase the finger pressure until the string bears firmly against the desired fret.

The increase in finger pressure to achieve good contact increases asymptotically as the point of finger contact moves farther from the desired fret. Good contact becomes unachievable at some point, varying with fret position, instrument, and player. This results from the increasing obstruction which the unwanted fret presents to finger depression.

The musician must therefore develop the technique of applying varying pressures to the strings, according to the location of the point of finger contact in the zone between the desired fret and the adjacent fret; he must develop the endurance to apply the required finger pressure for prolonged periods; and he must develop calluses on his fingertips it withstand the otherwise painful bearing pressures occasioned when the point of finger contact is a significant distance from the selected fret.

Instances of bowed necks, a chronic problem in conventional instruments, result in increased finger pressures required for clear tones because bowing upsets the normal fingerboardto-string geometry. Bowing is almost invariably in the direction encouraged by string tension, i.e., toward a hollow fingerboard, raising the strings away from the fingerboard. This has the effect of an increased taper of the string plane relative to the fret plane. The effective increased taper results in a need for an even greater depression of the string after contact with the unwanted fret to point of contact with the desired fret. If the bridge should be lowered to compensate for this, it will result in inadequate clearance and buzzing when frets in the upper register are employed.

Any discrepancy is one or more frets lying outside a fiat plane will result in some degree of additional effort by the player. However, manufacture and/ or maintenance of an instrument in which frets can be fixed in a perfect plane is beyond the current state of the art. Neck straightening mechanisms are often incorporated, but these devices can only work in the direction of reestablishing the optimum flat plane; they work against the neck as a unit and therefore cannot correct local out-of-plane conditions.

Stringed instruments of the prior art seem not to have been addressed to the foregoing problems. Those which employ movable frets apparently do so to achieve some special musical effect, as in U.S. Patent No. 2,489,657; or to simultaneously engage all strings with one fret, as in U.S. Patent No. 1,727,230; or to adjust the vibrational length of a string by some ancillary or added lever, button, key or the like not directly associated with the act of depressing the string for engagement with a fret, as in U.S. Patent No. 2,368,256.

SUMMARY OF THE INVENTION The present invention provides a system of movable frets for stringed musical instruments, in which each fret is movable toward an associated string as that string is depressed to thereby reduce the amount of finger pressure required to provide firm engagement between the string and the fret.

The present system can be incorporated in the stringed instrument at the time of manufacture, and it can also be employed with existing stringed instruments by replacement of the instrument fingerboard with a fingerboard including the present system of movable frets. When fitted to the stringed instrument, the present system permits the musician to utilize normal playing techniques, without having to manipulate auxiliary devices during playing to achieve the desired reduction in required finger pressure. In the preferred embodiment there are no levers, buttons, keys, or the like which protrude outside of the conventional dimensional envelope of the instrument.

The system provides a plurality of frets arranged across the guitar neck and constituting a fret set comparable to the conventional fret, and a plurality of these sets are spaced along the length of the guitar neck at the same locations as the conventional frets.

The upper surfaces of the frets lie in a static fret plane located below the plane of the strings, and are selectively urged upwardly toward an associated string by means of an actuator. Preferably the actuator takes the form of an elongated element positioned closely adjacent a string and extending between a pair of longitudinally spaced frets. The upper surface of the actuator is preferably located below the string plane and the actuator is so located that When the musician depresses a string to effect engagement of the string with a particular fret, the actuator associated with that fret is automatically depressed by the finger. The acuator is suitably coupled to the fret upper surface so that as the string and actuator are depressed, there is a corresponding upward movement of the fret upper surface, with firm engagement between the fret upper surface and the string occurring in a plane located above the static fret plane. Such engagement occurs with substantially the same finger pressure, regardless of the location of the point of engagement of the actuator by the players finger. Moreover, it will be apparent that the amount of finger pressure is reduced because the selected fret is moved upwardly sufficiently that the associated string is engaged in a plane high enough above the static fret plane that string depression is not obstructed by the next adjacent fret. Consequently, the amount of finger pressure required to effect the desired string depression is substantially unchanged, regardless of what the proximity may be between the unwanted fret and j the point of engagement of the players finger with the actuator.

Summarizing the primary objects of the present invention, the system reduces the finger pressures required to play a fretted stringed instrument, reduces the variations in finger pressures required relative to variance in finger positions between frets, alleviates the greater finger pressure requirements normally occasioned by an instrument having a bowed neck, and permits finger placement farther away from the selected fret. The individual frets are each selectively movable to engage the associated string at a point which largely eliminates the possibility of an adjacent, unwanted fret acting :as a barrier to proper seating of the string on the selected fret.

Other objects and features of the invention will become apparent from consideration of the following description taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a top plan view of the neck of a Spanish guitar incorporating the system of the present invention;

FIG. 2 is an enlarged top plan view of a portion of the system of FIG. 1, illustrating a fret operative to engage an associated guitar string;

FIG. 3 is a side elevational view of the portion of the system that is shown in FIG. 2, the fret being illustrated in its normal position, in which it is out of engagement with the associated string;

FIG. 4 is'a view taken along the line 4-4 of FIG. 2, and also illustrating in dotted outline the operative position of the fret in engagement with the associated string;

FIG. 5 is a view taken along the line 5-5 of FIG. 4;

FIG. 6 is a view taken along the line 66 of FIG. 4; FIG. 7 is an enlarged perspective view of the actuator support bracket; and

FIG. 8 is an enlarged view of the spring for urging the actuator and the fret toward the positions illustrated in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT E Referring now to the drawings, there is illustrated a portion of a usual and conventional Spanish guitar which has been modified in accordance with the present invention. This modification consists in substitution of a fingerboard 10 in place of the usual fingerboard. The fingerboard 10 could thus be .a replacement for the fingerboard of an existing guitar, or could be installed :as part of the original guitar. Moreover, although the invention will be described in conjunction with a Spanish guitar, it will be apparent that the invention is applicable for use in conjunction with .a variety of fretted instruments which are played by pressing the strings upon frets to thereby con trol the note or chord resulting when the depressed string is plucked or otherwise played.

The fingerboard 10 is preferably an integral element attachable by an adhesive or other suitable means to the upper surface of the guitar neck 12. The fingerboard 10 .4 includes a plurality of adjacent, elongatedgrooves or channels 14 corresponding in number with the number of strings 16 of the guitar, aligned therewith, and located directly beneath the strings 16.

The fingerboard 10 also includes a plurality of transversely oriented, longitudinally spaced channels extending across the longitudinal channels 14, and which are each characterized by a base 18 and a pair of opposed sloping or inclined abutments 20 and 22. The transverse channels are shallower than the longitudinal channels 14 so that the bases 18 and abutments 20 and 22 of each transverse channel are discontinuous, providing a pair of side-by-side bases 18 and pairs of side-by-side abutments 20 and 22 on the opposite sides of each channel 14.

At the intersection of each longitudinal channel 14 with one of the transverse channels there is located an arcuate fret 24 so that, for the six stringed Spanish guitar illustrated, there are six frets 24 extending transversely acros the guitar neck 12 to form a set which is generally equivalent to the conventional continuous fret of the usual Spanish guitar. These sets of frets 24 are longitudinally spaced along the neck of the guitar, as best illustrated in FIG. 1.

With each fret 24 there is associated an elongated, longitudinally oriented lever or actuator 26 generally aligned with the associated string 16 and subjacent channel 14. As will be seen the actuator 26 extending between the adjacent .pair of longitudinally spaced frets 24 is adapted for downward movement upon depression of the associated string 16, and the downward movement of the actuator 26 initiates an upward, pivotal movement of the adjacent fret 24 so that the string 16 does not have to be pressed downwardly with the force formerly required in guitars of the prior art. That is, the guitar fingering constitutes a depression of the desired string 16 in combination with a simultaneous raising of the adjacent fret 24. The particular mechanism by which the fret 24 is raised in response to depression of the actuator 26 will be described in detail later.

Each fret 24 is generally arcuate in configuration and includes an inclined, substantially fiat lower end 28 and a generally rounded upper end 30, the upper ends 30 of the frets 24 lying generally in a static fret plane 32 located below the plane of the strings 16. As best viewed in FIGS. 2 and 4, the outer surface of each fret 24 is rounded or arcuate to form bearing surfaces at the ends of the fret for slidable movement on the abutments 20 and 22 during partial rotation of the fret 24. The portion of the fret 24 between the rounded ends projects radially outwardly to define a central band 34 which extends more deeply into the associated channel 14, with the edges or shoulders of the band 34 engaging the sides of the channel 14 to constrain the fret 24 against lateral move ment.

The upper terminus of the band 34 forms a ledge 36 located adjacent the fret upper end 30, and this ledge is engaged by a spring 38 which tends to maintain the fret in the normal position illustrated in FIG. 3. However, as will be seen, the spring 38 is biasable upwardly to permit partial rotation of the fret to the dotted position illustrated in FIG. 4.

More particularly, the bias means or fret spring 38 for each fret, as best viewed in FIGS. 4, 5 and 8, fits within its associated channel 14 and extends generally longitudinally of the channel. The spring 38 includes a flat, generally horizontal platform 40 which at one lon gitudinal edge includes a pair of depending legs 42 which terminate in horizontally disposed base portions 44 which rest upon the base or floor of the channel 14. The opposite longitudinal edge of the platform 40 includes a pair of upwardly projecting spring sections 46 having reversely formed ends which engage the underside of the superjacent actuator 26. The spring sections 46 also engage the confronting side of a depending positioning portion 48 which is integral with the actuator 26.

With this arrangement, whenever the actuator 26 is depressed from the full line position to the dotted line position illustrated in FIG. 5, engagement between the underside of the actuator 26 and the spring sections 46 causes the spring sections 46 to be biased downwardly. The bias developed by such deformation tends to move the actuator upwardly to return it to the position illustrated in full line in FIG. 5.

The engagement of the spring sections 46 with the portion 48 of the actuator 26 also tends to constrain the actuator 26 from lateral movement toward the spring 38. As will be seen, movement of the actuator 26 in the opposite lateral direction is constrained by engagement between the actuator 26 and a support bracket 50.

The spring 38 includes a U-shaped longitudinal extension 52 integral with one end margin of the platform 40, the free end of the extension 52 terminating in a reversely formed and backwardly projecting tab 54. The tab 54 is the portion of the spring 38 which rests upon the ledge 36 of the fret 24 to bias it downwardly, as previously mentioned. The spring 38 therefore performs the dual function of biasing both the actuator 26 and the fret 24 to the full line position thereof illustrated in FIGS. 4 and 5.

In addition to the depending portion 48, each actuator includes an integral upward portion which is generally L-shaped in configuration, including an upright finger portion 56 for engagement by the musicians fingers, and a horizontally oriented portion 58, as best viewed in FIGS. 4 through 7. The depending portion 48 fits between a pair of longitudinally spaced end tabs 60 integral with the opposite ends of the support bracket 50, and the bracket 50 together with the actuator portion 48 fits within the associated longitudinal channel -14 next to the spring 38. As will be seen, the bracket 50 not only locates and retains the actuator 26 in position in the channel 14, but also cooperates with the spring 38 to define a fulcrum or axis of pivotal movement for the actuator 26.

The bracket end tabs 60 are integral with a vertically oriented bracket portion 62 which rests against the adjacent wall of the channel 14. The lower margin of the portion 62 also integrally includes a pair of longitudinally spaced tongues 64 which extend downwardly toward the base of the channel 14, transversely of the base, and then slope upwardly into engagement with the side of the channel 14 opposite the side against which the portion 62 rests. The resilient tongues 64 terminate in edges which tend to dig into and seat in the channel Wall to maintain the support bracket 50 in position in the channel 14. This permits the bracket 50 to be pressed into position within the channel 14 in a manner which makes inadvertent removal of the bracket 50 from the channel 14 improbable.

Also forming an integral part of the lower margin of the bracket portion 62 is a stop or element 66 which is located between the tongues 64 and also extends transversely. However, instead of engaging the opposite wall, the element 66 extends upwardly into engagement with a side of the actuator portion 48, and thus serves as a stop to maintain the actuator 26 in the position illustrated in FIG. 5. In effect, the element 66 resiliently opposes the biasing action of the spring section 46, which tends to pivot the actuator in a clockwise direction.

As best viewed in FIG. 5, the upper margin of the bracket portion 62 is bent inwardly of the channel 14 and seats within a longitudinal groove 68 provided in the side of the actuator 26. The upper margin of the portion 62 is further bent or deformed outwardly for engagement with the underside of the horizontal portion 58 of the actuator, thereby supporting the actuator against downward movement in the area and providing a fulcrum about which pivotal movement of the actuator can occur.

Consequently, depression of the actuator portion 56 by the musician pivots the actuator downwardly to the dotted position illustrated in FIG. 5, the pivotal movement taking place generally about an axis extending along the centerline of the longitudinal groove 68 in the actuator 26. Thus, the rotation takes place about the rounded surface of the reversely formed upper margin of the bracket 50.

Summarizing the interrelation of each set of fret 24, actuator 26, spring 38, and bracket 50', the actuator 26 is oriented and supported in position by the bracket 50, which constrains the actuator 26 against longitudinal movement, transverse movement, downward and upward movement in the area of the upper margin of the bracket, and upward movement relative to the upper extremity of the bracket 50'.

The spring 38 biases the actuator finger portion 56 to the full line position illustrated in FIG. 5, also biases the fret 24 downwardly for clockwise rotational movement to the full line position illustrated in FIG. 4, and constrains the actuator 26 against transverse movement. Moreover, since the lower end 28 of each fret 24 underlies its associated actuator 26, the spring 38 and the actuator cooperate to maintain the fret 24 in position within its channel 14.

The finger portion 56 of the actuator 26 is so located that it is depressed by the musicians finger when the finger depresses the adjacent string 16. Such depression of the string 16, and rising of the fret 24 occasioned by the movement of the actuator 26, results in engagement between the fret and the string in a plane which is located above the static fret plane 32. The point of engagement thus brings the string away from interference with the adjacent fret 24.

The musical instrument is played by pressing the strings 16 downwardly in the usual manner, the act of pressing a finger against a particular string 16 serving not only to depress the string but also to engage and depress the associated actuator 26. The continued depression of the string and the actuator 26 pivots the actuator generally about the fulcrum provided by the upper margins of the support bracket 50, the actuator moving downwardly against the bias of the spring 38.

Depression of the actuator 26 causes it to rotate the fret 24 upwardly against the tab 54 of the associated spring 38. The upwardly moving upper end 30 of the fret 24 meets the downwardly moving string 16 to effect the desired fretting. This occurs prior to the time that the string 16 is depressed to the point of engagement with the next adjacent or unwanted fret 24.

When the player raises his finger from the string 16, the bias of the spring 38 returns the fret 24 and the actuator 26 to the positions illustrated in full line in FIG. 4.

It is to be understood that the bias means 38 described above is merely exemplary and that the present invention comprehends other means for urging the components to their normal positions illustrated in full lines. Moreover, other means could be used to transmit movement of the actuator to the fret, it being important primarily that the interconnection or coupling be sufliciently solid that objectionable buzzing and rattling are eliminated.

I claim:

1. In a musical instrument having a tensioned string, the improvement comprising:

a fret movable toward and away from said string; and an actuator adjacent said fret and movable by the playing finger of the musician upon depression by the finger of that portion of said string adjacent said fret, said actuator being operative upon such movement to effect movement of said fret toward said string for engagement therewith.

2. The improvement of claim 1 and furthe including a bias means tending to urge said fret away from said string.

3. The improvement of claim 1 and further including a bias means tending to urge said actuator toward said string.

4. The improvement of claim 1 and including fingerboard means defining a fret receptacle below said string and having a pair of abutments engaged by said fret, said fret being rotatable upon said abutments upon engagement by said actuator whereby a portion of said fret is movable upwardly toward said string.

5. The improvement of claim 1 and including at least a pair of said frets spaced along the length of said string, and wherein said actuator is located below and generally aligned with said string, and extends between said frets for engagement by the musicians fingers anywhere in the intervening space between said frets.

6. The improvement of claim 1 wherein said actuator is elongated along the longitudinal axis of said string; and including a support bracket on edge of said actuator for pivotal movement of said actuator generally about said edge.

7. The improvement of claim 1 wherein said musical instrument includes a plurality of said tensioned strings, wherein said improvement includes a plurality of groups of said frets and actuators spaced along the length of said strings, and wherein each of said groups includes a plurality of frets and actuators arranged beneath and transversely of said strings, respectively.

8. The improvement of claim 7 wherein the structure of said improvement lies wholly beneath said strings.

9. The improvement of claim 7 wherein said musical instrument is a Spanish guitar and the structure of said improvement lies wholly within the dimensional envelope of said guitar.

References Cited V UNITED STATESPATENTS 577,930 3/1897 Prince .84-318 1,727,230 9/1929 Cox 84314 2,368,256 1/1945 McBride 84-315 RICHARD YB. wrLKINsoN, Primary Examiner LAWRENCE R. FRANKLIN, Assistant Examiner f2;;3' UNITED STATES PATENT OFFECE CERTIFICATE OF CORRECTION Patent No. q 1 69 1489 Dated September 30, 9 9

Inventofla) QARL EARTH It 16 certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected an ehown below;

4 line 45' delete "2" and insert --'-3--. g e lee "U-sha )ed" and insert -.-U-'shape--. delete "position" and insert -pos1tions Column 5, line i HF- -C 1- wlsgngnq I 1mm 1:; eam; m.

I I i l a g SfiWFM Patents .u 4...... t-....- vt Column '4, l lirie l9, delete "acres" and insert "across- Column 5, line 21

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US577930 *Jan 27, 1896Mar 2, 1897 Czar prince
US1727230 *May 23, 1927Sep 3, 1929Cox John E PFinger board for stringed musical instruments
US2368256 *Mar 16, 1942Jan 30, 1945John W McbrideStringed musical instrument
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3894468 *Aug 23, 1974Jul 15, 1975Dunlap Philip AStringed instrument with sliding variably spaced frets
US4189974 *Sep 22, 1978Feb 26, 1980Fathergill Rex DGuitar neck assembly
US4297936 *Apr 9, 1980Nov 3, 1981Mouton Martin JRetractable fret system for stringed instruments
US4620470 *Apr 24, 1985Nov 4, 1986Vogt Walter JFingerboard for stringed instruments
US4777858 *Apr 14, 1986Oct 18, 1988Petschulat David JAdjustable string contact system for a musical instrument
US7423208 *Aug 13, 2007Sep 9, 2008Muncy Gary OStringed instrument and associated fret mapping method
U.S. Classification84/314.00R, 984/115
International ClassificationG10D3/00, G10D3/06
Cooperative ClassificationG10D3/06
European ClassificationG10D3/06